1. Technical Field
This invention relates to the art of gas analysis and, more particularly, to instantaneous on-line analysis of gas flows having multicomponents.
2. Description of the Prior Art
Gas analysis has wide ranging utility, from the measurement of respiration of humans or animals to the measurement of the effluence of combustion chambers, including automotive emissions. Gas analysis has conventionally been accomplished by the use of dilution tubes and by the use of liquids or solids off-line from the flow of gases under analysis. These techniques are inadequate for modern purposes because of the inability to provide instantaneous dynamic information and measure only a single component per technique. These techniques are unable to process increasingly larger volumes of data.
Analyses without liquids or solids have included chemiluminescence, flame ionization, and total hydrocarbon analysis, all without the use of infrared spectroscopy. These modes have proved inadequate because (a) the analysis is of a single component, (b) takes too long, sometimes weeks, (c) the data for separate componenets has no commonality in response time and thus cannot be readily combined, (d) the sensed data suffers from cross-interferences of the added chemicals, and (e) some gaseous compounds cannot be analyzed.
One of the more recent adaptations for gas analysis has been the use of infrared spectroscopy. Although infrared spectroscopy has been used as a quality control technique to obtain information on the composition of chemical products for many years, it has been used essentially off-line and primarily for measurement of nongases. Samples are typically prepared as thin films or solutions and measured in a quality control room with a laboratory instrument. Unfortunately, inherent time delays between actual material production and analytical results can typically range from a few hours to several days, which can result in costly waste and production of unacceptable material. Fourier-transform, infrared spectrometric techniques have been applied to particles suspended in gas flows (see U.S. Pat. No. 4,652,755).
In those prior art applications where infrared spectroscopy was applied to gas analysis, there was no dilution of the gas sampler and therefore the gas itself had to be heated to a temperature in excess of 100.degree. C. to accommodate samples with high water vapor. If other reference information was applied to such detected information, the reference information had to be taken at identical elevated temperatures, which made the entire methodology extremely complex, delicate and difficult to calibrate. In U.S. Pat. No. 4,549,080, filters were used to look at isolated wavelengths, again without dilution.
The task of measuring emissions from vehicles has become increasingly more difficult. Demands for lower detection limits have arisen from the development of more efficient catalytic converters. Greater versatility is required for work with alternate fuels as new and as yet uncharacterized gas species are encountered. In addition to these requirements, a need for more efficient engines with lower emission rates necessitates the development of fast, on-line instrumentation, capable of analysis during transient engine operation. Such new analysis will permit in-depth examination of the combustion process in lieu of the current cumulative information obtained from conventional emissions instrumentations having expensive exhaust handling equipment including constant volume sampling.
Therefore, specific goals of this invention comprise providing an apparatus and method for constant volume sampling of a gas stream, which (i) eliminates the expense, size inefficiency, and inflexibility of large systems used heretofore, (ii) provides more improved accurate testing at normal atmospheric conditions and eliminates false data characteristic of prior sampling systems, (iii) provides a mass emission rate (rather than merely a concentration value of a selected chemical constituent, and (iv) can be used with any chemical sensing system. The elimination of water condensation contamination and the assurance of proportionality of mass flow rate in the sampled gas are most important.
The inventors herein have applied infrared spectroscopy to the on-line analysis of gases, particularly auto emissions. Our earlier work, as described in scientific publication "On-Line Characterization of Vehicle Emissions by FTIR and Mass Spectrometry", Butler et al, SAE Paper #810420 (1981), describes a system for dynamic analysis of vehicle emmissions; the analysis system was comprised of a fourier transform, infrared spectrometer, a quadropole mass spectrometer, and a total hydrocarbon analyzer. Although it allowed on-line measurement of regulated and nonregulated emissions from a steady-state gas stream, the system needed to be calibrated with some difficulty. The three major apparatus components were significantly expensive; but, most importantly, an unusually large size, constant volume sampling apparatus was required for dilution of the sample gas. The speed at which such an integrated system operated was at the rate of three seconds. However, the data was analyzed off-line, rendering an analysis not in real time (while the test is on-going). This introduces an analysis time which is not considered sufficiently fast for the demands of new applications. If the total hydrocarbon analyzer, quadropole mass spectrometer, and constant volume sampling unit could be eliminated, the cost of the system would be significantly reduced. If the remaining components could be improved in response time, the speed of data collection could be increased significantly. Furthermore, if the data could be processed in real time (during the test), the utility of information would be greatly enhanced because adjustments can be made immediately and effects of the adjustments can be seen.
An additional goal of this invention is to provide a combination apparatus of the new sampling apparatus herein with a chemical sensing system of the FTIR type. Such combination apparatus is an on-line measuring apparatus for multicomponent or single component gas emission flows, the apparatus being characterized by improved data collection speed, greater freedom from false or interference data, and is much less costly to fabricate.